Increased levels of circulating ICAM-1, VCAM-1, and L-selectin in obstructive sleep apnea syndrome

Endothelial function in obstructive sleep apnea and response to treatment

Impaired endothelium-dependent vascular relaxation is a prognostic marker of atherosclerosis and cardiovascular disease. We evaluated endothelium-dependent flow-mediated dilation (FMD) and endothelium-independent nitroglycerin (NTG)-induced dilation of the brachial artery with Doppler ultrasound in 28 men with obstructive sleep apnea (OSA) and 12 men without OSA. Subjects with OSA (apnea-hypopnea index; mean +/- SD, 46.0 +/- 14.5) had lower FMD compared with subjects without OSA (5.3 +/- 1.7% vs. 8.3 +/- 1.0%, p < 0.001), and major determinants of FMD were the apnea-hypopnea index and age. There was no significant difference in NTG-induced dilation. Subjects with OSA were randomized to nasal continuous positive airway pressure (nCPAP) or observation for 4 weeks. Subjects on nCPAP had significant increase in FMD, whereas those on observation had no change (4.4% vs. -0.8%, difference of 5.2%, p < 0.001). Neither group showed significant change in NTG-induced vasodilation. Eight subjects who used nCPAP for over 3 months were reassessed on withdrawing treatment for 1 week. On nCPAP withdrawal, FMD became lower than during treatment (p = 0.02) and were similar to baseline values. Our findings demonstrated that men with moderate/severe OSA have endothelial dysfunction and treatment with nCPAP could reverse the dysfunction; the effect, however, was dependent on ongoing use.

Nocturnal oxygen desaturation correlates with the severity of coronary atherosclerosis in coronary artery disease

STUDY OBJECTIVES

It has been suggested that sleep-disordered breathing (SDB) is a risk factor for ischemic heart disease, and may be associated with increased morbidity and mortality due to cardiovascular disease. The aim of this study was to examine the relation between nocturnal oxygen desaturation (NOD) due to SDB and the Gensini score, which is given to define the severity of coronary atherosclerosis, based on coronary angiograms findings, in patients with coronary artery disease.

DESIGN

We examined the NOD index (ODI) (desaturation of > 3%/events per hour) using pulse oximetry in 59 consecutive patients with coronary artery disease (ejection fraction, > 40%) that was diagnosed by coronary angiography, 30 patients with angina pectoris and 29 patients with old myocardial infarction. The Gensini score was calculated for each patient from the coronary arteriogram. The patients were classified into the following three groups according to the severity of oxygen desaturation: ODI of < 5 events per hour (group N; 16 patients); ODI of > or = 5 but < 15 events per hour (group A; 27 patients); and ODI of > or = 15 events per hour (group B; 16 patients). The groups then were examined for the relation between the ODI and the Gensini score.

RESULTS

Of the total number of patients, 72.9% had a nocturnal ODI of more than five events per hour. The Gensini score was significantly higher in groups A and B than in group N, and showed a significant positive correlation with the ODI (R = 0.45; p = 0.01) in all patients. Multiple regression analysis showed that the ODI was the most significant, independent determinant of the Gensini score among the coronary risk factors tested, and that it explained 13.4% of the variance.

CONCLUSION

These findings suggest that NOD due to SDB may be an important contributor to coronary atherosclerosis in the patients with cardiovascular disease.

Collapsible upper airway segment to study the obstructive sleep apnea/hypopnea syndrome in rats

Animal models have been used to study the pathophysiology of the obstructive sleep apnea/hypopnea syndrome (SAHS). Nevertheless, in none of the models described to date have the animals been subjected to the different patterns of upper airway obstructive events (apneas, hypopneas, and inspiratory flow limitation) characterizing SAHS. Our aim was to devise and test a computer-controlled collapsible upper airway segment applicable to rats and able to realistically mimic obstructive SAHS events. The collapsible segment (total volume <2 cm(3) and a dead space of approximately 0.25 cm(3)) consisted of a Starling resistor based on a latex membrane subjected to an external pressure applied by a computer-controlled pressure source. The collapsible segment was tested in eight anaesthetized and tracheostomized rats. The upper airway segment allowed us to induce obstructive apneas and hypopneas with flow and inspiratory effort waveforms similar to the ones observed in patients with SAHS. This collapsible upper airway segment may be a useful tool to implement a rat model of SAHS.

Cardiovascular consequences of obstructive sleep apnea

Sleep apnea is associated with several cardiovascular disease conditions. A causal relationship between sleep apnea and each of these diseases is likely, but remains to be proven. The clearest evidence implicating OSA in the development of new cardiovascular disease involves data that show an increased prevalence of new hypertension in patients with OSA followed over 4 years [3]. Circumstantial evidence and data from small study samples suggest that OSA, in the setting of existing cardiovascular disease, may exacerbate symptoms and accelerate disease progression. The diagnosis of OSA always should be considered in patients with refractory heart failure, resistant hypertension, nocturnal cardiac ischemia, and nocturnal arrhythmias, especially in individuals with risk factors for sleep apnea (e.g., central obesity, age, and male gender). Treating sleep apnea may help to achieve better clinical control in these diseases and may improve long-term cardiovascular prognosis.

Sleep-disordered breathing and stroke

Sleep-related breathing disorders are strongly associated with increased risk of stroke independent of known risk factors. The direction of causation favors sleep-disordered breathing leading to stroke rather than the other way around, although definitive proof of this awaits the results of prospective cohort studies. If causal, even a moderately elevated risk of stroke coupled with the high prevalence of sleep-disordered breathing could have significant public health implications. The relationship between sleep-disordered breathing and stroke risk factors is complex, and likely part of the risk for cerebrovascular events is because of higher cardiovascular risk factors in patients with increased RDI. The mechanisms underlying this increased risk of stroke are multi-factorial and include reduction in cerebral blood flow, altered cerebral autoregulation, impaired endothelial function, accelerated atherogenesis, thrombosis, and paradoxic embolism. Because of the effects of sleep-disordered breathing on vascular tone, hypertension is believed to be a major mechanism by which sleep-disordered breathing might influence risk of stroke. Because sleep-related breathing disorders are treatable patients with stroke/TIA should undergo investigation, with a thorough sleep history interview, physical examination, and polysomnography. Treatment of sleep apnea has been shown to improve quality of life, lower blood pressure, improve sleep quality, improve neurocognitive functioning, and decrease symptoms of excessive daytime sleepiness [98]. Further treatment trials are needed to determine whether treatment improves outcome after stroke and whether treatment may serve as secondary prophylaxis and modify the risk of recurrent stroke or death.

Obstructive sleep apnoea syndrome--an oxidative stress disorder

Obstructive sleep apnoea syndrome (OSA) is associated with increased cardiovascular morbidity and mortality. However, the underlying mechanisms are not entirely understood. This review will summarize the evidence that substantiates the notion that the repeated apnoea-related hypoxic events in OSA, similarly to hypoxia/reperfusion injury, initiate oxidative stress. Thus, affecting energy metabolism, redox-sensitive gene expression, and expression of adhesion molecules. A limited number of studies substantiate this hypothesis directly by demonstrating increased free radical production in OSA leukocytes and increased plasma-lipid peroxidation. A great number of studies, however, support this hypothesis indirectly. Increase in circulating levels of adenosine and urinary uric acid in OSA are implicated with increased production of reactive oxygen species (ROS). Activation of redox-sensitive gene expression is suggested by the increase in some protein products of these genes, including VEGF, erythropoietin, endothelin-1, inflammatory cytokines and adhesion molecules. These implicate the participation of redox-sensitive transcription factors as HIF-1 AP-1 and NFkappaB. Finally, adhesion molecule-dependent increased avidity of OSA monocytes to endothelial cells, combined with diminished NO bioavailability, lead to exaggerated endothelial cell damage and dysfunction. Cumulatively, these processes may exacerbate atherogenic sequelae in OSA.

Effects of obstructive sleep apnea on circulating ICAM-1, IL-8, and MCP-1

Obstructive sleep apnea syndrome (OSAS) is one of the most important risk factors of cardiovascular disorders. In the treatment of OSAS, nasal continuous positive airway pressure (nCPAP) has been widely used and found to be effective. In the present study, we hypothesized that the hypoxic stress caused by obstructive sleep apnea would increase circulating intercellular adhesion molecule-1 (ICAM-1), interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1) in untreated OSAS patients compared with an age-matched control group. In addition, we hypothesized that nCPAP may decrease OSAS-induced hypoxic stress and mediators. To examine these hypotheses, we measured circulating ICAM-1 and IL-8 before and after nCPAP therapy in OSAS patients. We observed that nCPAP decreased apnea, desaturation, and the circulating ICAM-1 and IL-8 levels in OSAS patients. The circulating levels of ICAM-1, IL-8, and MCP-1 in untreated OSAS patients were significantly greater than those in the controls. These observations suggest that nCPAP therapy could reduce OSAS-induced hypoxia and generation of inflammatory mediators. Treatment of OSAS using nCPAP can be, therefore, a potential approach to decrease risk of the progression of OSAS-associated disorders.

Adhesion molecules in patients with coronary artery disease and moderate-to-severe obstructive sleep apnea

STUDY OBJECTIVES

It has been suggested that obstructive sleep apnea (OSA)-induced hypoxic stress might contribute to cardiovascular disorders by promoting expression of soluble adhesion molecules. The reported increase of circulating adhesion molecules in patients with OSA remains controversial because confounders such as cardiovascular risk factors and left ventricular function have not been adequately controlled for. We hypothesized that soluble intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, L-selectin, and E-selectin levels are correlated with OSA independent of coexisting coronary artery disease (CAD).

SETTINGS

University-affiliated teaching hospitals.

DESIGN AND PARTICIPANTS

A prospective study of 61 consecutive subjects with angiographically proven CAD deemed to have stable angina.

INTERVENTIONS

Fifteen patients (mean +/- SD) 61.2 +/- 1.9 years old with moderate-to-severe OSA (apnea-hypopnea index [AHI] > or = 20/h) were matched to a control group (AHI < or = 5/h) for age, gender, body mass index, and severity of CAD. Venous blood samples were collected the morning of the sleep study and assayed for human ICAM-1, VCAM-1, L-selectin, and E-selectin with commercially available enzyme-linked immunosorbent assay kits.

RESULTS

All but L-selectin were significantly increased in the OSA group compared to the control subjects (ICAM-1, 367.4 +/- 85.2 ng/mL vs 252.8 +/- 68.4 ng/mL, p = 0.008; VCAM-1, 961.5 +/- 281.7 ng/mL vs 639.1 +/- 294.4 ng/mL, p = 0.004; E-selectin, 81.0 +/- 30.4 ng/mL vs 58.1 +/- 23.2 ng/mL, p = 0.03, respectively). The increased levels of adhesion molecules correlated with the AHI and the oxygen desaturation index but not with the severity of hypoxemia or the frequency of arousals.

CONCLUSIONS

These findings suggest that OSA modulates the expression of proinflammatory mediators. Further studies should evaluate the influence of adhesion molecules on cardiovascular outcome in CAD patients with OSA.

Increased adhesion molecules expression and production of reactive oxygen species in leukocytes of sleep apnea patients

Obstructive sleep apnea (OSA) is associated with increased cardiovascular morbidity and mortality. Free radicals and adhesion molecules were implicated in the pathogenesis of atherosclerosis leading to cardiovascular disorders. Therefore, we investigated the link between CD15, CD11c, CD11b, and CD64 expression on leukocytes and their ability to generate reactive oxygen species (ROS) in patients with OSA and control volunteers. We also studied the effects of hypoxia in vitro on monocytes from control subjects and the ability of monocytes from both groups to adhere to human endothelial cells in culture. The effect of nasal continuous positive airway pressure (nCPAP) treatment was studied as well. We found that OSA was associated with increased expression of adhesion molecules CD15 and CD11c on monocytes, increased adherence of monocytes in culture to human endothelial cells, increased intracellular ROS production in some monocyte and granulocyte subpopulations, and upregulation of CD15 expression due to hypoxia in vitro in monocytes of control subjects. Furthermore, nCPAP treatment was associated with downregulation of CD15 and CD11c monocyte expression and decreased basal ROS production in CD11c+ monocytes. Monocyte adherence to endothelial cells decreased as well. Our findings provide one of the possible mechanisms for explaining the high rate of cardiovascular morbidity in patients with sleep apnea.

Free radicals in the physiological control of cell function

At high concentrations, free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concentrations, however, nitric oxide (NO), superoxide anion, and related reactive oxygen species (ROS) play an important role as regulatory mediators in signaling processes. Many of the ROS-mediated responses actually protect the cells against oxidative stress and reestablish "redox homeostasis." Higher organisms, however, have evolved the use of NO and ROS also as signaling molecules for other physiological functions. These include regulation of vascular tone, monitoring of oxygen tension in the control of ventilation and erythropoietin production, and signal transduction from membrane receptors in various physiological processes. NO and ROS are typically generated in these cases by tightly regulated enzymes such as NO synthase (NOS) and NAD(P)H oxidase isoforms, respectively. In a given signaling protein, oxidative attack induces either a loss of function, a gain of function, or a switch to a different function. Excessive amounts of ROS may arise either from excessive stimulation of NAD(P)H oxidases or from less well-regulated sources such as the mitochondrial electron-transport chain. In mitochondria, ROS are generated as undesirable side products of the oxidative energy metabolism. An excessive and/or sustained increase in ROS production has been implicated in the pathogenesis of cancer, diabetes mellitus, atherosclerosis, neurodegenerative diseases, rheumatoid arthritis, ischemia/reperfusion injury, obstructive sleep apnea, and other diseases. In addition, free radicals have been implicated in the mechanism of senescence. That the process of aging may result, at least in part, from radical-mediated oxidative damage was proposed more than 40 years ago by Harman (J Gerontol 11: 298-300, 1956). There is growing evidence that aging involves, in addition, progressive changes in free radical-mediated regulatory processes that result in altered gene expression.

Plasma homocysteine levels in obstructive sleep apnea: association with cardiovascular morbidity

OBJECTIVES

Obstructive sleep apnea (OSA) is associated with cardiovascular morbidity and mortality. Plasma levels of homocysteine are also associated with cardiovascular morbidity and mortality. We therefore investigated homocysteine and conventional cardiovascular risk factors in OSA patients with and without cardiovascular morbidity in comparison with normal control subjects and ischemic heart disease (IHD) patients without OSA.

SETTING

Technion Sleep Medicine Center, Haifa, Israel.

METHODS AND PARTICIPANTS

Levels of homocysteine, cholesterol, low-density lipoprotein, high-density lipoprotein, triglycerides, creatinine, vitamins B(12) and B(6), and folic acid were determined in 345 participants after overnight fasting. These included OSA patients with IHD (n = 49), with hypertension (n = 61), or without any cardiovascular disease (n = 127). Two control groups were employed: IHD patients without or with low likelihood for sleep apnea (n = 35), and healthy control subjects (n = 73).

RESULTS

After adjustment for age, body mass index, creatinine, and existence of diabetes mellitus, OSA patients with IHD had significantly higher homocysteine levels (14.6 +/- 6.77 micromol/L) than all other groups including the IHD-only patients. Hypertensive OSA patients had comparable homocysteine levels to IHD patients (11.80 +/- 5.28 micromol/L and 11.92 +/- 5.7 micromol/L, respectively), while patients with OSA only had comparable levels to normal control subjects (9.85 +/- 2.99 micromol/L and 9.78 +/- 3.49 micromol/L, respectively). No differences in conventional cardiovascular risk factors or in vitamin levels were found between groups.

CONCLUSIONS

Patients with the combination of IHD and OSA have elevated homocysteine levels. We hypothesize that these results may be explained by endothelial dysfunction combined with excess free-radical formation in OSA patients.

Effects of nasal continuous positive airway pressure on soluble cell adhesion molecules in patients with obstructive sleep apnea syndrome

PURPOSE

Obstructive sleep apnea syndrome is common in middle-aged men and may be associated with an increased risk of cardiovascular disease. We investigated the effect of nasal continuous positive airway pressure (CPAP) treatment on levels of soluble cell adhesion molecules-which have been shown to be associated with the development of atherosclerosis-in these patients.

SUBJECTS AND METHODS

We studied 23 patients with obstructive sleep apnea syndrome diagnosed by polysomnography who were treated with nasal CPAP. Serum soluble intercellular adhesion molecule-1, E-selectin, and vascular cell adhesion molecule-1 levels were measured before nasal CPAP was started, and after 3 or 4 days (n = 19), 1 month (n = 23), or 6 months (n = 11) of treatment.

RESULTS

After 3 to 4 days of nasal CPAP therapy, the mean (+/- SD) soluble E-selectin level had decreased from 89 +/- 44 ng/mL to 69 +/- 28 ng/mL (P = 0.002). After 1 month, the soluble intercellular adhesion molecule-1 level had decreased from 311 +/- 116 ng/mL to 249 +/- 74 ng/mL (P = 0.02). After 6 months, soluble vascular cell adhesion molecule-1 levels had not changed significantly, while the mean soluble intercellular adhesion molecule-1 level (212 +/- 59 ng/mL) had decreased further (P = 0.02). Before treatment, soluble intercellular adhesion molecule-1 levels and the apnea and hypopnea index were correlated (r = 0.43, P = 0.04).

CONCLUSIONS

Obstructive sleep apnea and hypopnea have a significant adverse effect on serum soluble cell adhesion molecule-1 levels that may be reduced by nasal CPAP treatment.

Enhanced release of superoxide from polymorphonuclear neutrophils in obstructive sleep apnea. Impact of continuous positive airway pressure therapy

Obstructive sleep apnea (OSA) is associated with increased cardiovascular morbidity and mortality. Free oxygen radicals have been implicated in the pathogenesis of cardiovascular disorders. Therefore, we aimed to test the hypothesis that increased oxidative stress constitutes one underlying mechanism for the connection between OSA and cardiovascular disease. In 18 patients with OSA the release of superoxide from polymorphonuclear neutrophils was determined after stimulation with the bacterial tripeptide formylmethionylleucylphenylalanine (fMLP) and the calcium ionophore A23. Superoxide production was measured as superoxide dismutase-inhibitable reduction of cytochrome c. Blood samples were obtained before and after two nights of CPAP therapy and after 4.8 +/- 0.6 mo of follow-up. Ten healthy young volunteers and 10 lung cancer patients without OSA but a similar spectrum of comorbidity served as controls. Before CPAP, neutrophil superoxide generation was markedly enhanced in OSA when compared with both control groups. Effective CPAP therapy led to a rapid and long-lasting decrease of superoxide release in OSA. In conclusion, OSA is linked with a "priming" of neutrophils for enhanced respiratory burst. The increased superoxide generation, which might have major impact on the development of cardiovascular disorders, is virtually fully reversed by effective CPAP therapy.